Air blast circuit breaker



April 1959 H. FoRwALb 2,881,291

' AIR BLAST CIRCUIT BREAKER Filed D60. 10, 1956 INVENTOR. f/aa k on Forwa 1d g aw United States Patent 2,881,291 AIR BLAST CIRCUIT BREAKER Haakon Forwald, Ludvika, Sweden, assignor to Allmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application December 10, 1956, Serial No. 627,158 Claims priority, application Sweden December 15, 1955 1 Claim. (Cl. 200-148) 'The present invention concerns an air blast circuit breaker of the type which comprises an air container permanently filled with air in which the breaking point is arranged and on opening the breaking gap an are formed between the pair of contacts is subjected to an extinguishing flow of air generated by the pressure prevailing in the container when the air is allowed to flow out through an air blast valve which is so designed that the members of the valve are held in closed position by a force acting in the opposite direction to the pressure prevailing in the container.

The invention relates particularly to such circuit breakers where the stationary contact of the breaking gap is carried by an insulator in the container and in which the movable contact of the breaking pair consists of a pneumatically operated nozzle shaped contact which is telescopically movable in a metal cylinder in the container and in which at the end remote from the stationary con tact, a tightening device for an outlet valve of the container is arranged, which valve opens in the direction of flow of the extinguishing air. The invention is chiefly characterised in that the distance between the said tight ening device at the outlet of the container and the stationary Contact, only to a small extent exceeds the sum of the maximum breaking distance between the contacts and the length of the nozzle part of the movable contact. Whereby the space between the contact point and the outlet opening will have a favorable form with respect to the air stream and will form the least possible space for the accumulation of cool air.

An improvement of the arc extinction is gained by the invention because, on opening the blast valve the cool air on the outlet side of the contact pair, having a maximum outlet speed through an opening at a given relation between the pressures, being less than the maximum escape speed for the gases heated by the arc, is rapidly removed and will not form a stopper preventing the flow of the gases heated by the arc and therefore will not decrease the extinguishing effect. The advantages gained are that all members of the valve necessary for the operation of the contacts and the valves are arranged entirely outside the space formed between the contact point and the seating surface of the valve so that this space will form a short, straight channel having the least possible length.

The invention is most readily understood by reference to the accompanying drawing which shows a movable contact with its valve member and operating member, a stationary contact and the part of the wall in the compressed air container in which the contacts are arranged. On the drawing, 1 designates the compressed air container and 2 and 3 reinforcing flanges welded to the wall of the container. 4 designates the stationary contact enclosed in the container which contact is carried by an insulator not shown in the drawing. By means of the screws 5 a gear casing is attached to the reinforcing flange 2 of the container. A metal cylinder 7 is, by means of screws 8, rigidly joined with the upper part of the gear casing 6. The lower part of the gear casing is closed by a cover 9 attached by means of screws 10. 11 is a valve member axially movable in the gear casing 6 which member in its lower part is formed as a piston sliding tightly against the inner cylindrical wall of the casing 6, the said piston being provided with a packing ring 15. The valve member 11 tightly engages against a seating ring 12 and is operated in the closing direction by means of the spring 13 and the pressure prevailing in the inner space 14 in the casing 6. The space 39 in the casing extends around the valve member 11 and is, by a number of openings 40 in the casing wall, in permanent communication with the atmosphere. The valve member 11 is provided with a central opening for a rod 16 which rigidly connects the movable nozzle contact 17 of the breaking pair with a valve member 18 arranged in the space 14, which member, when the breaker is open, is in contact with the sealing ring 19 of the cover 9. The contact 17 is telescopically movable in the metal cylinder 7 and is actuated in the closing direction by a spring 21 which rests against the ring 22 and the ring 23 joined to the contact 17. 41 designates a packing ring arranged in the cylinder 7. The space 14 in the gear casing 6 is, by the channels 24 and 25, in communication with the compressed air container. 26 is a throttle valve through which the flow of air through said channels 24 and 25 can be controlled. The air conduits 28 and 29 join the valve 27 with the compressed air container 1 and space 14. By means of the valve 27 the space 14 is alternatively brought into communication with the compressed air container and the atmosphere. The valve member 30 is, by the rod 31 joined with the membrane 32. The space 33 below the membrane 32 may, by the operating valve 34, be brought into communication with the operating pipe line 35 or the atmosphere. 37 designates a number of sliding contacts for the transmission of current from the gear casing to the movable contact 17, and these sliding contacts are forced against the movable contact by a number of springs 38 and are arranged in the annular shaped space which is formed between the upper part of the metal cylinder 7 and the piece 36 joined to it.

The arrangement acts in the following way. The circuit breaker is opened by delivering air from the operating line 35 over the operating valve 34 to the space 33 below the membrane 32, so that the valve member 30 is lifted and tightly forced against the end of the conduit 28. The space 14, below the valve member 11 which, when the circuit breaker is closed contains air of the same pressure as the container, is then by the conduit 29 and the valve 27 in communication with the open air and is rapidly emptied. The valve member 11 and the nozzle contact 17 are then, by the pressure in the container 1, forced downwards which opens the outlet opening in the upper part of the casing 6. The valve member 18 is forced against the sealing ring 19 in the cover 9 when the movable contact 17 reaches its lower position and interrupts the communication between the space 14 and the atmosphere so that the space 14 is filled with air from the container through the channels 24 and 25. The pressure in the space 14 will then act on the valve member 11 in a closing direction so that the outlet opening is closed and also acts downwardly on the valve member 18 so that the contact 17 is retained in open position. In this position the lower nozzle formed part of the contact 17 will be in immediate proximity to the seating ring 12 so that the distance between the outlet opening and the stationary contact exceeds to only a very small extent, the sum of the contact distance and the length of the contact.

The circuit breaker is closed when the space 33 is emptied through the valve 34 so that the valve member 30 will again take the position illustrated in the figure. The space below the valve member 11 will then be in communication with the container so that the pressure on both sides of the valve member will be equal. The retaining force will then disappear and a movable contact 17 is moved against the stationary contact 4 by means of the spring 21 so that the breaking gap is closed.

I claim as my invention An air blast circuit breaker having a container for the permanent accommodation of compressed air, and comprising a stationary contact, an air valve opening in the said container, a cylinder secured to the interior of the casing in line with the stationary contact and having an open end communicating with the said valve opening, 15

a casing arranged externally of the container and in alignment with the said cylinder, a movable contact arranged to slide in said cylinder and having a nozzle shaped part for engagement with the said stationary contact and for movement into close proximity to the said air valve opening, a spring concentrically arranged outside the said cylinder for pressing the said nozzle shaped part against the stationary contact, and a valve member arranged to slide in said casing and to close the said valve opening, the total distance between said valve opening and the stationary contact being substantilly equal to the distance moved by said nozzle shaped part plus the longitudinal length of the nozzle shaped part in the direction of the air flow therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 2,574,334 Latour Nov. 6, 1951 2,747,055 Forwald May 22, 1956 2,766,348 Forwald Oct. 9, 1956 

